From Malt Waste to Watts and Biofertilizer

By Mark Hale | October 24, 2018

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Muntons Malted Ingredients Inc. is well known to the U.S. food industry as the supplier of “Great British Malt.” The Chicago-based company’s products are used in the brewing and baking trades, as well as in breakfast cereals, confectionery and a wide range of other food products. What is less known is that Muntons’ U.K. parent company is a leader in sustainable production. Since early 2016, the company has operated a novel, closed-loop system that turns some 88,000 tons of liquid malt waste into a high- quality biofertilizer at its production plant at Stowmarket in Suffolk, England.

The basis of the system is a $7.5 million, 499-kilowatt, on-site anaerobic digestion (AD) plant that generates 25 percent of the facility’s electricity. Since it was commissioned, the system has treated almost 33 million gallons of effluent, saving the company more than $3.35 million in electricity and waste disposal costs, and reduced carbon emissions by 800 tons of CO2e. Each year, the plant turns 88,000 tons of liquid malt waste into quality organic digestate fertilizer, which is used by the company’s network of growers to produce some of the 275,000 tons of barley needed to make 198,000 tons of Muntons’ malt each year.

Muntons has sustainability at its core, and first became interested in AD after analysis showed that 60 percent of its supply chain’s carbon footprint came from the artificial fertilizer used by its barley growers. The company realized if a proportion of the liquid waste it produces every year could be treated through AD, it could produce a high-quality organic biofertilizer for its farmers to use instead, significantly reducing its carbon footprint.

The new treatment removed the need for these journeys, and also captured nutrients—such as phosphate—that were previously lost when treated effluent was discharged into the river. The digestate product is high in organic matter and acts as a soil conditioner and improver. It can also be applied to land over a longer period of time than the liquid waste previously used.

Working to No WasteMuntons’ digestate is blended with low-chemical oxygen demand (COD) effluent before being treated with Dissolved Air Flotation in the existing activated sludge plant. This stabilizes the digestate and removes further COD, nitrates and phosphorus prior to the effluent being discharged to local waterways in accordance with an environmental permit. The remaining sludge is then pasteurized in a three-tank unit from HRS Heat Exchangers, and used as biofertilizer.

The HRS system works on a three-tank principle: While one tank is being filled, the second tank holds the sludge at 158 degrees Fahrenheit, and the third tank is being emptied (each process lasts one hour). Waste cooling water from the combined-heat-and-power engine is used to heat the sludge in corrugated tube-in-tube heat exchangers, which is more efficient than heating an entire tank of digestate. HRS also incorporated an energy recovery section into the process to make it even more efficient: Energy is transferred from the hotter, pasteurized sludge to the colder, unpasteurized sludge, reducing energy consumption by up to 70 percent compared to conventional, which would otherwise be wasted. It also has the advantage of being able to run at a half-flow rate, should the volume of digestate stock reduce, and the equipment’s monitoring features ensure that every batch of digestate can be traced back to the feedstock from which it was produced.

Once pasteurized, the biofertilizer can be dewatered if required, and supplied for application as a liquid for soil injection or a solid for muck spreading. Analysis by Muntons has shown that its biofertilizer is higher in nitrogen, potash and sulfur than most other available biosolids, as well as being a good source of phosphate and magnesium. The biofertilizer is used on local land from which the company sources its malting barley, but Muntons is also keen to stimulate the wider biofertilizer market.

Muntons is also working with the University of Lincoln on a project to document the composition and effectiveness of the biofertilizer. This has initially demonstrated that lettuce grown with Muntons’ biofertilizer demonstrates quality and growth benefits over artificial fertilizers of similar nutrient concentration. A further collaboration with University College London revealed that the digestate yields a type of bacteria that produces an antibiotic that kills multidrug-resistant E. coli bacteria.

Ensuring Digestate QualityBecause Muntons’ plant uses a combination of both anaerobic and aerobic processes, for technical reasons, the resulting sludge cannot be certified as meeting the U.K. standards for compost and digestate. The standards, known as PAS110, provide a guarantee to users that the digestate product meets certain quality parameters, and mean that it is exempt from further waste legislation and can be applied to fields as a fertilizer. However, the process includes a pasteurization step, and the resulting material is treated in accordance with the requirements of the PAS110 standard for anaerobic digestate, based on conventional Hazard Analysis Critical Control Points principles. This helps assure local farmers that the final biofertilizer contains no ergot or plant pathogens contaminants.

According to Muntons’ environment manager, a pasteurization system from HRS Heat Exchangers was a crucial part of the entire process, as the company wanted the biofertilizer to compete in the agricultural market with the likes of PAS110 digestate and other biosolids that have undergone pasteurization. Even though considered low-risk and all feedstock is from traceable food grade grains, Muntons felt that pasteurizing its material was the best way to help the company get End-of-Waste Certification, and reassure local farmers their land will not be contaminated with ergot or plant pathogens.

Muntons commissioned a 3-Tank Batch Sludge Pasteurizer Systems with energy recovery from HRS to treat the anaerobic and aerobic wastes. Almost 200m3 (53,000 gallons) of high-liquid waste, with a high COD, is treated each day and as well as the CO2 savings, the project has saved Muntons more than $3.35 million in energy and disposal costs to date. Although the material cannot be certified to PAS110, it has been granted End-of-Waste Certification by the U.K. Environment Agency, meaning that it can be used as a biofertilizer.

Matt Hale, international sales and marketing director at HRS, commented, “For Muntons this whole project has been about maximizing efficiency. Although they have an abundance of heat, they still wanted to recapture what they could, and our heat exchangers provide 40 percent heat regeneration. Our system also allows the tanks to run at half flow rates if necessary, meaning they can still carry on pasteurizing without having to wait to build up a stock of digestate. Working with a company like Muntons to deliver a truly revolutionary waste treatment plant shows exactly what is possible in terms of implementing the circular economy. The results that the biofertilizer is providing in trials and in the field show just what a valuable resource it is, and this success could be repeated elsewhere around the world.”